It is found experimentally that the electric field in a certain region of Earth's atmosphere is directed vertically down. At a certain location, at an altitude of 508 m the electric field has magnitude 19.6 N/C and at an altitude of 780 m the magnitude is 76.0 N/C. Find the net amount of charge contained in a cube with horizontal faces at altitudes of 508 and 780 m. Neglect the curvature of Earth. Give your answer in the form of "+/-a.bc x 10^(x) C PLEASE SHOW WORK